Signal monitoring and control system for an optical navigation sensor

ABSTRACT

A circuit and method are provided to control the strength of signals from an array of photo-detectors (PDs) in an optical navigation sensor. The circuit includes a number of transimpedance-amplifiers (TIAs) each coupled to an output of at least one PD to receive a current signal therefrom and generate a signal in response thereto. A controller coupled to outputs of the TIAs receives the signals and executes an algorithm to adjust gain of a signal processor coupled to the array. In one embodiment, the signal processor includes differential transimpedance-amplifiers (DIFF-TIAs) each including inputs coupled to receive current signals from the array, and the controller outputs a control signal to adjust a time over which the DIFF-TIAs and the TIAs integrate the current signals. Optionally, the signal processor includes gain-amplifiers coupled to the DIFF-TIAs and TIAs, and the controller outputs a signal to adjust gain thereof.

TECHNICAL FIELD

The present disclosure relates generally to a user interface device, and more particularly to a user interface device including an optical navigation sensor and a guard-sensor to enable the optical navigation sensor.

BACKGROUND

Optical navigation sensors are commonly used in devices, such as an optical computer mouse, trackball or touch pad, for interfacing with personal computers and workstations. One technology used for optical navigation sensors relies on sensing light reflected from a surface using an array of photosensitive elements or detectors, such as photodiodes. Generally, outputs of the individual elements in the array are combined using signal processing circuitry to detect and track motion of a pattern or image in the reflected light and from that tracking to derive the motion of the surface relative to the array.

The optical navigation sensor described above will receive very weak signals when tracking on dark surfaces, and is subject to signal saturation when tracking on light surfaces. When this happens, the estimation of displacements become erratic and unreliable, hence affecting the overall performance of the optical navigation sensor.

SUMMARY

A gain control circuit is used to control strength of signals from an array of photo-detectors (PDs) in an optical navigation sensor. Generally, the circuit includes a number of transimpedance-amplifiers (TIAs) each comprising an input coupled to at least one of the PDs in the array to receive a current signal therefrom and generate an automatic gain control (AGC) signal in response thereto, and a controller coupled to outputs of the number of TIAs to receive the AGC signal therefrom. The controller includes logic to execute a signal gain adjustment algorithm and to adjust a gain of a signal processor coupled to the array of PDs in response to the AGC signal.

BRIEF DESCRIPTION OF THE DRAWINGS

These and various other features of the control system and method will be apparent upon reading of the following detailed description in conjunction with the accompanying drawings and the appended claims provided below, where:

FIG. 1 is a functional block diagram of an optical navigation sensor including a gain control circuit;

FIG. 2 is a schematic block diagram illustrating a gain control loop in an optical navigation sensor;

FIGS. 3A and 3B illustrate embodiments of a signal gain adjustment algorithm;

FIG. 4 is a schematic block diagram illustrating coupling of a transimpedance-amplifier (TIA) of the gain control circuit to an array in an optical navigation sensor;

FIG. 5 is a schematic block diagram of an array, signal processor and gain control circuit receiving an automatic gain control signal (AGC) from a signal strength algorithm executed in the signal processor; and

FIG. 6 is a schematic block diagram illustrating a plurality of TIAs of the gain control circuit, each coupled to a number of photo-detectors (PDs) located in different contiguous areas of the array.

DETAILED DESCRIPTION

The present disclosure is directed generally to optical navigation sensors and more particularly to a control circuit and method for use with an optical navigation sensor included in an input device to sense displacement of the device relative to a surface.

Optical navigation sensors, for example, an optical computer mouse, trackballs, and the like, may input data into and interface with personal computers and workstations. For purposes of clarity, many of the details of optical navigation sensors in general and optical sensors for optical devices, such as an optical computer mouse, trackball or touch pad, in particular that are widely known and are not relevant to the present control system and method have been omitted from the following description. Optical navigation sensors are described, for example, in commonly assigned U.S. Pat. No. 7,138,620, entitled, “Two-Dimensional Motion Sensor,” by Jahja Trisnadi et al., issued on Nov. 21, 2006.

A gain control circuit and method of the present disclosure monitors and controls strength of signals from an array in an optical navigation sensor used to sense movement of the optical navigation sensor, or device in which it is included, relative to a surface. The array, which comprises multiple photosensitive elements, such as photodiodes (PDs), determines a direction and magnitude of movement by detecting changes in a pattern of light reflected from the surface. Generally, the circuit includes a number of transimpedance-amplifiers (TIAs) each comprising an input coupled to at least one PD in the array to receive a current signal therefrom and generate an automatic gain control (AGC) signal in response thereto. A controller coupled to outputs of the TIAs adjusts or modulates gain in a signal processor of optical navigation sensor coupled to the array and/or modulates an intensity of illumination of the surface to control strength of signals from the array.

The signal processing method of the present disclosure is applicable to both speckle and non-speckle based optical navigation sensors comprising either one or more one-dimensional (1D) arrays or one or more two-dimensional (2D) arrays of PDs. The 2D array may be either a periodic, 2D comb-array, which includes a number of regularly spaced photosensitive elements comprising 1D or 2D periodicity, a quasi-periodic 2D array (such as one comprising Penrose tiling), or a non-periodic 2D array, which has a regular pattern but doesn't include periodicities.

In an embodiment, the optical navigation sensor is a speckle-based system, which senses movement based on displacement of a complex intensity distribution pattern of light, known as speckle. Speckle is the complex interference pattern generated by scattering of coherent light off a rough surface and detected by a photosensitive element, such as a photodiode, with a finite angular field-of-view (or numerical aperture). However, it will be appreciated by those skilled in the art that the method and circuit of the present disclosure is not limited to speckle-based systems, and can be used with other types of illumination, including coherent and non-coherent light sources, and images in which the signal captured by the optical navigation sensor comprises a strong spatial frequency matching a period or spacing of PDs in the array.

A functional block diagram of an optical navigation sensor including a gain control circuit is shown in FIG. 1. Referring to FIG. 1, an optical navigation sensor 100 generally includes a light source or illuminator 104, such as a Vertical-cavity surface-emitting laser (VCSEL), and illumination optics 106 to illuminate a portion of a surface 108, imaging optics 110 to map or image a pattern in light reflected by the surface, and an array 112 to sense or detect change in the pattern. Although shown in the figure as ellipses resembling a lens, the illumination optics 106 and imaging optics 110 can include any number of lenses, prisms, and reflectors to illuminate the surface 108 or the array 112. The array 112 includes one or more two-dimensional (2D) arrays each comprising a number of photosensitive elements, such as photodiodes (PD) 114, on which light reflected from the surface 108 is received. Current signals from PDs 114 in the array 112 are combined by a signal processor 116 to provide measurements or data (Δx, Δy data 118) on the magnitude and direction of displacement of the optical navigation sensor 100 or an input device, such as an optical computer mouse, in which it is included relative to the surface 108. The optical navigation sensor 100 further includes a gain control circuit 120 for controlling the signal processor 116 and/or the illuminator 104 to automatically control strength of signals originating from the array 112.

The gain control circuit will now be described in detail with reference to FIGS. 2 and 3, where FIG. 2 illustrates a gain control loop of the gain control circuit in an optical navigation sensor, and FIGS. 3A and 3B illustrate methods of generating an automatic gain control (AGC) signal according to embodiments.

Referring to FIG. 2, in one embodiment the gain control circuit 202 includes one or more current-to-voltage converters, such as a single-ended, transimpedance-amplifier (TIA 204) to receive a current signal from a number of PDs 206 in an array 208 and generate an AGC signal that is coupled to a controller 210 in the gain control circuit. Each of the TIAs 204 is directly coupled to PDs 206 extending across the array 208 to substantially eliminate errors that can arise when monitoring signals originate from PD located outside a contiguous area of the array.

The AGC signal output by the TIA 204 is an output voltage signal given by the expression AGC=g*I_(IN), where g is a predetermined gain having units in volts/ampere, and I_(IN) is the current signal received from the PDs 206.

The controller 210 includes computer circuitry or logic to execute a signal gain adjustment algorithm and to adjust a gain in a signal processor 212 coupled to the array 208 in response to the AGC signal. Generally, as in the embodiment shown, the signal processor 212 includes a number of differential transimpedance amplifiers (DIFF-TIAs 214) each comprising inputs coupled to number of PDs 216 in the array 208 to receive current signals therefrom and output a voltage signal (V_(OUT)) generated in response to a difference between the received current signals. V_(OUT) is given by the expression V_(OUT)=g*(I_(IN+), −I_(IN−)), where g is a predetermined gain having units in volts/ampere, and I_(IN+) is the current applied to a non-inverting input and I_(IN−) is the current applied to an inverting input. The signal processor 212 also includes one or more amplification stages 218 following the DIFF-TIAs 214 to amplify the voltage signals generated by the DIFF-TIAs and output quasi-sinusoidal signals or waveforms (CC, CS, SC, SS), which are further processed in the signal processor to provide data on the magnitude and direction of displacement of the optical navigation sensor relative to the surface. Where the amplification stages 218 include single ended amplifiers, as shown, the output signal (V_(SIG) _(—) _(OUT)) can be expressed as follows: V_(SIG) _(—) _(OUT)=G*V_(IN), where G is a predetermined unitless gain of the amplifier, and V_(IN) is the input voltage received from the DIFF-TIAs 214. In another embodiment (not shown), the amplification stages 218 can include differential amplifiers having a second input coupled to a predetermined reference or offset voltage. In this embodiment, the output signal is expressed as V_(SIG) _(—) _(OUT)=G*(V_(IN1)−V_(IN2)) where V_(IN1) is the voltage applied to one of the inputs and V_(IN2) to another.

In one version of this embodiment, the controller 210 is configured to output an integration time control signal to adjust or modulate an integration time over which the DIFF-TIAs 214 integrate the received current signals to generate the voltage signals, thereby adjusting gain in the signal processor 212. If the AGC signal is too weak, below a specified or predetermined minimum, the controller 210 executing the signal gain adjustment algorithm operates to increase the time over which the DIFF-TIAs 214 integrate the received current signals, thereby increasing gain in the signal processor 212 and reducing if not eliminating errors in the displacement data. Conversely, if the AGC signal is too strong or exceeds a specified or predetermined maximum, the controller 210 decreases the time over which the DIFF-TIAs 214 integrate the received current signals, thereby avoiding errors in the displacement data that can result from saturating amplifiers in the signal processor 212.

Optionally or additionally, where the signal processor 212 further includes one or more amplification stages 218 following the DIFF-TIAs 214, the controller 210 is configured to output an amplification gain control signal to adjust or modulate gain of the amplification stages. If the AGC signal is below the predetermined minimum the controller 210, executing the signal gain adjustment algorithm operates to increase gain in the amplification stages 218. If the AGC signal exceeds the predetermined maximum, the controller 210 decreases gain in the amplification stages 218.

In certain embodiments, the controller 210 can be configured to output an illuminator driver setpoint control signal to adjust or modulate illumination from an illuminator (VCSEL 220). In particular, the illuminator driver setpoint control signal is coupled to a driver (VCSEL driver 222) used to power the illuminator (VCSEL 220). The controller 210 executes the signal gain adjustment algorithm and operates the VCSEL driver 222 to increase electrical power applied to the illuminator (VCSEL 220), or to increase a duty-cycle of the VCSEL driver 222 if the AGC signal is below the predetermined minimum and to decrease the applied power or duty-cycle if the AGC signal exceeds the predetermined maximum.

Although the controller 210 and the signal gain adjustment algorithm executed therein is described above as controlling a single parameter, i.e., an integration time, amplification stage gain or illumination intensity, it will be appreciated that the controller 210 and algorithm can be operated to simultaneously or sequentially modulate one or more of these parameters to control the strength of signals from the array 208. For example, in certain embodiments, such as those used in a wireless computer mouse, the controller 210 and algorithm can be configured to decrease power to the illuminator (VCSEL 220) or duty cycle of the VCSEL driver 222 if the AGC signal exceeds the predetermined maximum, thereby reducing power consumption. In the same embodiment, the controller 210 and algorithm can be configured to increase amplifier gain if the AGC signal is below a predetermined minimum, thereby increasing the dynamic range of a signal out of the array 208 while minimizing an increase in power consumption.

An aspect of the signal gain adjustment algorithm is the order in which adjustments to the illuminator power (or duty cycle), integration time and amplifier gain are made. An embodiment of the signal gain adjustment algorithm is illustrated in FIGS. 3A and 3B, where FIG. 3A is a flowchart illustrating increase of signal strength and where FIG. 3B is a flowchart illustrating decrease of signal strength. Referring to FIG. 3A, the order in the algorithm of adjustments used to increase signal is to adjust illuminator power first (block 302), then integration time (block 304), then amplifier gain (block 306). Illuminator power can be increased by increasing the duty-cycle or fraction of time in a given period in which power is applied to the illuminator. The amplifier gain can be increased by increasing a gain of one or more individual amplifiers or by switching one or more amplifiers into a chain of amplifiers in the amplification stage. The reverse of this order is used to decrease signal strength, thereby achieving an optimized signal-to-noise-ratio (SNR). Referring to FIG. 3B, the order of adjustments made in the algorithm to decrease signal is to adjust amplifier gain first (block 308), then integration time (block 310), then illuminator power (block 312).

In another embodiment of signal gain adjustment algorithm (not shown), the order of adjustments can be selected to reduce power consumption. In particular, to increase signal strength the order of adjustment can be to first adjust illuminator power, then amplifier gain and then integration time (i.e., VCSEL duty-cycle). Similarly, to the embodiment described above, a reverse order can be used to decrease signal. The order of adjustments used to decrease signal strength, while reducing power consumption and maintaining reasonable SNR, is to adjust integration time (i.e. VCSEL duty-cycle), then amplifier gain and finally illuminator power.

In other embodiments, the TIAs of the gain control circuit can be coupled in parallel with the DIFF-TIAs of the signal processor to shared PDs in the array. By shared PDs, it is meant PDs that are coupled directly to TIAs in the gain control circuit and are coupled to DIFF-TIAs in the signal processor. In one embodiment of this version, shown in the FIG. 4, each of the single-ended TIAs 402 in the gain control circuit is coupled to an input of one of the DIFF-TIAs 404 in the signal processor 406 to split off and route from the PDs 408 in the array 410 to the TIA. The TIA converts the current signal to a voltage to generate the AGC signal that is then coupled to a controller (not shown in this figure), which executes a signal gain adjustment algorithm and operates to adjust or modulate the integration time of the DIFF-TIAs, gain of an amplification stage 412, and/or intensity of illumination from an illuminator (not shown in this figure).

In another embodiment, shown in FIG. 5, the AGC signal is derived from DIFF-TIAs in the signal processor. Referring to FIG. 5, current signals from PDs 502 in the array 504 are converted to voltage signals by DIFF-TIAs 506 in the signal processor 508. The voltage signals are amplified in amplification stage 510 and the result processed using a signal strength calculation 512 or algorithm to determine signal strength of quasi-sinusoidal signals (CC, CS, SC, SS). As in the embodiments described above the AGC signal derived from signal strength calculation 512 is coupled to a controller 514, which executes a signal gain adjustment algorithm and operates to adjust or modulate the integration time of the DIFF-TIAs 506, gain of an amplification stage 510, and/or intensity of illumination from an illuminator (not shown in this figure). When used in speckle based optical navigation sensors this embodiment has the added advantage of enabling the gain loop to respond to reduction in signals (CC, CS, SC, SS) from the array 504 due to fading of detected speckle spatial frequencies. In addition, the AGC signal derived from signal strength calculation 512 is not affected by the stray-light, i.e., the light not reflected or scattered from a tracking surface, which may vary from part to part due to component placement tolerances.

The signal strength can be determined using a number of different calculations or algorithms including: (i) calculation of peak-to-peak amplitude; (ii) calculation of standard deviation; and (iii) calculation of an average of magnitudes squared of phasor vectors derived from the signals in logarithm scale (SIGLOG function) of the array.

Example embodiments of each of these different calculations or algorithms for determining signal strength from a comb-array in a speckle-based optical navigation sensor are described in detail below.

Consider a block of N sample frame pairs with T₁ and T₂ frame intervals from two sensor areas within an array (sensor1 and sensor2), each sample frame from each sensor area contains following signals output from the differential trans-impedance amplifiers: {CC,CS,SC,SS}_(k,t,s) where sub-index “k” denotes the location of a frame pair within the block (k=1, 2 . . . N); sub-index “t” denotes the T₁ or T₂ frame interval within a frame pair (t=T₁ or T₂); and sub-index “s” indicates which sensor area the signals come from (s=sensor1, or sensor2). The corresponding in-phase (I) and quadrature (Q) signals for processing motion along two diagonal directions (“+” and “−” directions) can be derived as follows: I _(+,k,t,s) =CC _(k,t,s) −SS _(k,t,s) Q _(+,k,t,s) =CS _(k,t,s) +SC _(k,t,s) I _(−,k,t,s) =CC _(k,t,s) +SS _(k,t,s) Q _(−,k,t,s) =CS _(k,t,s) −SC _(k,t,s)

The block-averaged motion across T₁ frame interval along the two diagonal directions can be estimated from the phase angles of the following “b-vectors”:

$b_{+ {,x,T_{1}}} = {\frac{1}{2N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\lbrack {{I_{+ {,k,T_{1}}} \times I_{+ {,{({k - 1})},T_{2}}}} + {Q_{+ {,k,T_{1}}} \times Q_{+ {,{({k - 1})},T_{2}}}}} \right\rbrack_{s}}}}$ $b_{+ {,y,T_{1}}} = {\frac{1}{2N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\lbrack {{Q_{+ {,k,T_{1}}} \times I_{+ {,{({k - 1})},T_{2}}}} - {I_{+ {,k,T_{1}}} \times Q_{+ {,{({k - 1})},T_{2}}}}} \right\rbrack_{s}}}}$ $b_{- {,x,T_{1}}} = {\frac{1}{2N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\lbrack {{I_{- {,k,T_{1}}} \times I_{- {,{({k - 1})},T_{2}}}} + {Q_{- {,k,T_{1}}} \times Q_{- {,{({k - 1})},T_{2}}}}} \right\rbrack_{s}}}}$ $b_{- {,y,T_{1}}} = {\frac{1}{2N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\lbrack {{Q_{- {,k,T_{1}}} \times I_{- {,{({k - 1})},T_{2}}}} - {I_{- {,k,T_{1}}} \times Q_{- {,{({k - 1})},T_{2}}}}} \right\rbrack_{s}}}}$ and the block-averaged motion across T₂ frame interval along the two diagonal directions can be estimated from the phase angles of the following “b-vectors”:

$b_{+ {,x,T_{2}}} = {\frac{1}{2N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\lbrack {{I_{+ {,k,T_{2}}} \times I_{+ {,k,T_{1}}}} + {Q_{+ {,k,T_{2}}} \times Q_{+ {,k,T_{1}}}}} \right\rbrack_{s}}}}$ $b_{+ {,y,T_{2}}} = {\frac{1}{2N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\lbrack {{Q_{+ {,k,T_{2}}} \times I_{+ {,k,T_{1}}}} - {I_{+ {,k,T_{2}}} \times Q_{+ {,k,T_{1}}}}} \right\rbrack_{s}}}}$ $b_{- {,x,T_{2}}} = {\frac{1}{2N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\lbrack {{I_{- {,k,T_{2}}} \times I_{- {,k,T_{1}}}} + {Q_{- {,k,T_{2}}} \times Q_{- {,k,T_{1}}}}} \right\rbrack_{s}}}}$ $b_{- {,y,T_{2}}} = {\frac{1}{2N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\lbrack {{Q_{- {,k,T_{2}}} \times I_{- {,k,T_{1}}}} - {I_{- {,k,T_{2}}} \times Q_{- {,k,T_{1}}}}} \right\rbrack_{s}}}}$ where the sub-index “x” and sub-index “y” denote the X and Y coordinates of the phasor diagram in which these “b-vectors” can be displayed; and “b_(x)” and “b_(y)” are the two components of a “b-vector” in the phasor diagram.

Thus, the peak-to-peak amplitude of the comb-array signals within a block of N sample frame pairs can be computed based on the following equation: A _(pp)=max {I _(+,k,t,s) Q _(+,k,t,s) ,I _(−,k,t,s) ,Q _(−,k,t,s)}_(k=1,2, . . . , N;t=T) ₁ _(,T) ₂ _(;s=sensor1,sensor2)−min {I _(+,k,t,s) ,Q _(+k,t,s) ,I _(−,k,t,s) ,Q _(−,k,t,s)}_(k=1,2, . . . , N;t=T) ₁ _(,T) ₂ _(;s=sensor1,sensor2)

Since these in-phase and quadrature signals are zero-mean, the standard deviation of the comb array signals within a block of N sample frame pairs can be calculated based on the following equation:

$A_{stddev} = \sqrt{\frac{1}{8N}{\sum\limits_{k = 1}^{N}\;{\sum\limits_{t = T_{1}}^{T_{2}}\;{\sum\limits_{s = {{sensor}\mspace{11mu} 1}}^{{sensor}\mspace{11mu} 2}\;\left\{ {\left( I_{+ {,k,t,s}} \right)^{2} + \left( Q_{+ {,k,t,s}} \right)^{2} + \left( I_{- {,k,t,s}} \right)^{2} + \left( Q_{- {,k,t,s}} \right)^{2}} \right\}}}}}$ and the comb array signal SIGLOG function is defined as the average of the magnitudes squared of the “b-vectors” mentioned above in logarithm scale:

${SIGLOG} = {4 \times {{LOG}_{2}\left\lbrack {\frac{1}{4}{\sum\limits_{t = T_{1}}^{T_{2}}\;\left\{ {\left( b_{+ {,x,t}} \right)^{2} + \left( b_{+ {,y,t}} \right)^{2} + \left( b_{- {,x,t}} \right)^{2} + \left( b_{- {,y,t}} \right)^{2}} \right\}}} \right\rbrack}}$

An embodiment of the SIGLOG function calculation is to take separate averages of the magnitudes squared of the “b-vectors” for the two orthogonal directions (“+” and “−” directions), and then take the minimum of the two averages. The SIGLOG function is this minimum in logarithm scale:

${SIGLOG} = {4 \times {{LOG}_{2}\left\lbrack {{MIN}\left\{ {\frac{{\sum\limits_{t = T_{1}}^{T_{2}}\;\left( b_{+ {,x,t}} \right)^{2}} + \left( b_{+ {,y,t}} \right)^{2}}{2},\frac{{\sum\limits_{t = T_{1}}^{T_{2}}\;\left( b_{- {,x,t}} \right)^{2}} + \left( b_{- {,y,t}} \right)^{2}}{2}} \right\}} \right\rbrack}}$

In another embodiment, shown in FIG. 6, the gain control circuit includes multiple TIAs 602A through 602D, each comprising an input coupled to a number of PDs 604 located in a contiguous area of an array 606 different from PDs coupled to another of the TIAs. The controller (not shown in this figure) further includes logic to execute an algorithm or perform a calculation to determine a spatial distribution of an intensity or level of light across the array 606 using AGC signals (AGC1-AGC4) from the TIAs 602A-602D. Information on the spatial distribution of light level across the array 606 can be used, for example, to determine a height and/or angle between the array and a tracking surface relative to which it is displaced. This information or measurement can also be used to determine if the optical navigation sensor, and more particularly the array 606, is properly assembled within manufacturing tolerances into an input device, such as a computer mouse, in which it is included. The embodiment illustrated in FIG. 6 show a configuration in which four different single-ended TIAs 602A-602D are each coupled to multiple PDs 604 in the array 606 to determine the light level or beam position across the array. However, it will be appreciated that other configurations including a greater or lesser number of TIAs or PDs coupled to each TIA can also be used without departing from the scope of the present disclosure.

For example, in one embodiment the TIAs 602 can include a number of TIAs coupled to one or small number of PDs 604 located near a peripheral edge of the array 606 outside of the area normally illuminated by light originating from the system illuminator and reflected from a tracking surface. These TIAs 602 coupled to PDs 604 near the edge of the array 606 can be used primarily or solely for determining a photocurrent due to stray light, i.e., light not reflected from a tracking surface, which can then be subtracted from a signal out of the TIAs 602 or DIFF_AMPs 608 to improve accuracy of the of the gain control circuit or optical navigation sensor. The TIAs 602 may include a number of TIAs coupled to one or small number of PDs 604 located near a center of the array 606 so the accuracy of the AGC signal derived from the outputs of the TIAs is less susceptible to component placement tolerances in assembly as well as changes in illuminator beam spot size.

In the description, for purposes of explanation, numerous specific details have been set forth in order to provide a thorough understanding of the control system and method of the present disclosure. It will be evident; however, to one skilled in the art that the present control system and method may be practiced without these specific details. In other instances, well-known structures, and techniques are not shown in detail or are shown in block diagram form in order to avoid unnecessarily obscuring an understanding of this description.

Reference in the description to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the control system or method. The appearances of the phrase “one embodiment” in various places in the specification do not necessarily all refer to the same embodiment. The term “to couple” as used herein may include both to directly connect and to indirectly connect through one or more intervening components.

The foregoing description of specific embodiments and examples have been presented for the purpose of illustration and description, and although described and illustrated by certain of the preceding examples, the signal monitoring method and control system disclosed herein are not to be construed as being limited thereby. They are not intended to be exhaustive or to limit the control system and method to the precise forms disclosed, and many modifications, improvements and variations within the scope of the disclosure are possible in light of the above teaching. 

What is claimed is:
 1. A gain control circuit to control strength of signals received from an array of photo-detectors in an optical navigation sensor, the gain control circuit comprising: a number of transimpedance-amplifiers (TIAs) each including an input coupled to an output of at least one photo-detector (PD) in the array to receive a current signal therefrom and to generate an automatic gain control (AGC) signal in response thereto; and a controller coupled to outputs of the number of TIAs to receive the AGC signal therefrom, the controller including logic to execute a signal gain adjustment algorithm and to adjust a gain of a signal processor coupled to the array of PDs in response to the AGC signal, wherein the signal processor comprises a number of differential transimpedance-amplifiers (DIFF-TIAs) each including inputs coupled to the array of PDs to receive current signals therefrom and to output a voltage signal generated in response thereto.
 2. A gain control circuit according to claim 1, wherein the controller is configured to output an integration time control signal to adjust an integration time of the number of DIFF-TIAs over which the received current signals are integrated to generate voltage signals.
 3. A gain control circuit according to claim 2, wherein the controller is further configured to output an integration time control signal to adjust an integration time of the number of TIAs over which the received current signals are integrated to generate voltage signals.
 4. A gain control circuit according to claim 1, wherein the signal processor further comprises a number of gain amplifiers coupled to outputs of each of the number of DIFF-TIAs and each of the number of TIAs, and wherein the controller is configured to output an amplifier gain control signal to adjust gain of the number of gain amplifiers.
 5. A gain control circuit according to claim 1, wherein the input of at least one of the number of TIAs is coupled in parallel with an input of at least one of the DIFF-TIAs to receive a portion of the current signal from the array of PDs coupled thereto.
 6. A gain control circuit to control strength of signals received from an array of photo-detectors in an optical navigation sensor, the gain control circuit comprising: a number of transimpedance-amplifiers (TIAs) each including an input coupled to an output of at least one photo-detector (PD) in the array to receive a current signal therefrom and to generate an automatic gain control (AGC) signal in response thereto; and a controller coupled to outputs of the number of TIAs to receive the AGC signal therefrom, the controller including logic to execute a signal gain adjustment algorithm and to adjust a gain of a signal processor coupled to the array of PDs in response to the AGC signal, wherein the optical navigation sensor is included in an input device to sense displacement of the input device relative to a surface and the optical navigation sensor further comprises an illuminator to illuminate at least a portion of the array with light reflected from the surface, and wherein the controller is configured to adjust illumination from the illuminator.
 7. A gain control circuit to control strength of signals received from an array of photo-detectors in an optical navigation sensor, the gain control circuit comprising: a number of transimpedance-amplifiers (TIAs) each including an input coupled to an output of at least one photo-detector (PD) in the array to receive a current signal therefrom and to generate an automatic gain control (AGC) signal in response thereto; and a controller coupled to outputs of the number of TIAs to receive the AGC signal therefrom, the controller including logic to execute a signal gain adjustment algorithm and to adjust a gain of a signal processor coupled to the array of PDs in response to the AGC signal, wherein the number of TIAs comprise a plurality of TIAs, each of the plurality of TIAs including an input coupled to a number of PDs located in a contiguous area of the array different from PDs coupled to another of the plurality of TIAs, and wherein the controller further includes logic to determine a spatial distribution of light level across the array of PDs using AGC signals from the plurality of TIAs.
 8. An optical navigation sensor to sense displacement of an input device relative to a surface, the optical navigation sensor comprising: an illuminator to illuminate at least a portion of the surface; an array of photo-detectors (PDs) to receive light reflected from the illuminated portion of the surface; a signal processor coupled to outputs of PDs in the array of PDs to integrate current signals received therefrom and output a voltage signal generated in response thereto; and a gain control circuit for controlling strength of signals from the array of PDs, the circuit including a number of transimpedance-amplifiers (TIAs) each including an input coupled to an output of at least one of the PDs in the array to receive a current signal therefrom and to generate an automatic gain control (AGC) signal in response thereto, and a controller coupled to outputs of the number of TIAs to receive the AGC signal therefrom, the controller configured to adjust an integration time of the signal processor over which the received current signals are integrated in response to the AGC signal.
 9. An optical navigation sensor according to claim 8, wherein the signal processor comprises a number of differential transimpedance-amplifiers (DIFF-TIAs) each including inputs coupled to outputs of PDs in the array of PDs.
 10. An optical navigation sensor according to claim 9, wherein the controller is further configured to output an integration time control signal to adjust an integration time of the number of TIAs over which the received current signals are integrated to generate voltage signals.
 11. An optical navigation sensor according to claim 10, wherein the signal processor further comprises a number of gain amplifiers coupled to outputs of each of the number of DIFF-TIAs and each of the number of TIAs, and wherein the controller is further configured to output an amplifier gain control signal to adjust gain of the number of gain amplifiers.
 12. An optical navigation sensor according to claim 9, wherein the signal processor further comprises a number of gain amplifiers coupled to outputs of each of the number of DIFF-TIAs, and wherein the controller is further configured to output an amplifier gain control signal to adjust gain of the number of gain amplifiers.
 13. An optical navigation sensor according to claim 8, wherein the controller is further configured to adjust illumination from the illuminator.
 14. A method of controlling strength of signals from an array of photo-detectors (PDs) in an optical navigation sensor, the method comprising: coupling to an input of at least one of a number of transimpedance-amplifiers (TIAs) a current signal from an output of at least one of the PDs in the array and generating an automatic gain control (AGC) signal in response thereto; coupling the AGC signal to a controller and executing therein a signal gain adjustment algorithm to generate control signals in response to the AGC signal; and coupling the control signals to a signal processor coupled to the array of PDs and adjusting a gain of the signal processor in response thereto, wherein the signal processor comprises a number of differential transimpedance-amplifiers (DIFF-TIAs) each including inputs coupled to the array of PDs to receive current signals therefrom and output a voltage signal generated in response thereto.
 15. A method according to claim 14, wherein adjusting the gain of the signal processor comprises adjusting an integration time of the number of DIFF-TIAs over which the received current signals are integrated to generate voltage signals.
 16. A method according to claim 15, wherein the controller is further configured to output an integration time control signal to adjust an integration time of the number of TIAs over which the received current signals are integrated to generate voltage signals.
 17. A method according to claim 15, wherein the signal processor further comprises a number of gain amplifiers, each coupled to the output of one of the number of DIFF-TIAs, and wherein adjusting the gain of the signal processor comprises adjusting a gain of the number of gain amplifiers.
 18. A method according to claim 14, wherein the optical navigation sensor is included in an input device to sense displacement of the input device relative to a surface and the optical navigation sensor further comprises an illuminator to illuminate at least a portion of the array with light reflected from the surface, and wherein the controller is further configured to generate an illumination control signal to adjust illumination from the illuminator. 